Ways to End the World

A friend recently asked me how I think the world might end. It’s a good question – lots of fun too, as a scientist. There seem to be countless ways to bring the world to an end – but here are some of the best ones we came up with. Feel free to add your own in the comments.

Nemesis!

Roughly every 30 million years something very bad seems to happen – life on Earth seems to die in vast quantities and a large percentage of all Earth’s species go extinct. Why do these mass-extinction events occur? Not sure – but it does seem to have happened with a reasonably regular interval for over 250 million years.

One hypothesis for this is that there is something ominous circling around us, at the edge of the Solar System. Some think it could be a large planet, other suggest a dead star – it has been given names like Planet X and Nemesis. Whatever it is, the theory goes that it is orbiting our Sun in a highly elliptical fashion. Once every orbit it plunges very close to the Sun, just scraping the edge of the Solar System: the Oort Cloud.

The Oort cloud is home to countless rocky bodies – it is the home of many comets – and such a massive gravitational nudge would send potentially thousands of these objects hurtling into the inner Solar System – one of which might hit us and cause a catastrophic global disaster. This might what killed the dinosaurs, and it’s possibly what will kill us.

Magnetic Switch

Since the mid-nineteenth century humans have been monitoring the Earth’s magnetic field. The same magnetic field that guides migratory birds and makes a compass work also protects us from harmful radiation from the Sun and gives us the beautiful Northern Lights. But here’s the thing – it is gradually weakening. According to some researchers, this could mean that something is about to change.

We also know – and this where it gets disturbing – that the Earth’s magnetic field has historically flipped over from time to time. In fact this usually happens every 250,000 years. It has been almost 800,000 years since the last flip so perhaps we’re overdue. Of course no one was around to witness the last one and so we don’t know what effect it would have. Things could get very ugly though.

If the magnetic field that protects the Earth did flip it would mean that somewhere along the way we wouldn’t be protected from space for a while! We might be bombarded with harmful radiation or cosmic rays. The lovely aurora would perhaps be slightly more menacing if they gave you cancer. If the flip is sudden then it would wreak havoc on the world’s electric systems – potentially frying them.

The Singularity

We are now able to make ever-smarter machines. What happens when we make a machine that is smarter than us? The answer surely is that it will be able to built an even better, smarter machine and that in turn will build an even better one too. Within a few cycles we will be faced with a machine so clever that we seem puny and irrelevant by comparison. The world could quickly be controlled and organised by such a machine and we will have ended our reign here.

We are also extending the human lifespan faster all the time (in the West) – what happens when we extend it by more than a year each year? We will then live indefinitely. Technological progress advances exponentially. This means that world-changing advancements come along at shorter and shorter intervals – eventually you reach a mathematical singularity, at which point things can no longer be thought of the way they used to.

The theory goes that some singularity is coming in the next century and although it may not be quite as we imagine it, it will possibly end the world as we know it. It may bring an end to our lives as we know them – in the machine case for example – why not download ourselves into super-intelligent machines and go onto bigger and better things? At our current rate of progress we will make more progress in the next century than in the past 10,000 years. The world as we understand it will surely cease to be.

Irradiated

Gamma Ray Bursts (GRBs) are distant but gargantuan explosions that take just a few seconds and release more energy than the Sun will in its entire lifetime! Some are 100s of times more powerful than that. Needless to say, you don’t need to be very close to one of these things to be more than a little singed. It could be almost anywhere in our galaxy and still devastate the planet.

There are other ways to be irradiated: the Sun could go nova, releasing massive quantities of dangerous material and radiation; a stray pulsar could accidentally spin around and fry us like an massive, errant laser pointer.

However it might happen, it remains remotely possible that in a brief instant the Earth could find itself totally irradiated on one side. Every living thing, every molecule of anything would be vapourised and instantly! Half the population – more or less – would be gone in a microsecond. And they’re the lucky ones. If you’re unfortunate enough to live on the other side of the Earth during this high-energy blast then you have the pleasure of gradually rotating around into the radiation – if it is still there. Worse still you could experience the awful, apocalyptic nightmare that is a shockwave of plasma – made up of every living thing from one half of the planet – sweeping across the world, incinerating everything as it goes.

Andromeda

We’ve all heard the old wives tale about the Sun dying and swallowing up the Earth as it becomes a red giant, right? Well let me tell you you don’t need to worry about it. That will take 6 billion years to happen – that’s ages! Especially whn there’s something much worse heading for us much faster.

The Andromeda Galaxy, the Milky Way’s friendly galactic neighbour and virtual twin sister is heading right for us. Pulled in by gravity, Andromeda and the Milky Way are on a collision course and in 2 or 3 billion years Andromeda will rip our galaxy apart like cotton wool. Shockwaves will ripple through the two galaxies, triggering supernovae and star formation at an incredible rate.

The Solar System will be lucky to survive such an event. Gravitational forces could tear us apart, radiation could fry us to a crisp or if we’re really unfortunate we could be gobbled up by one of two very big black holes as they coalesce and merge.

Snowball Earth

Periodically, many times over the course of the Earth’s history ice has covered the world and then gone again. I’m not talking about ice ages – no this is something even more dramatic. 600 million years ago the Earth was a giant snowball – entirely covered by ice. It also happened 100 million years before that and over two billion years ago. This ‘Snowball Earth’ is the result of a runaway cooling effect where the ice covering the surface of the planet increases the reflectivity (or albedo) such that a lot of the incident radiation from the Sun bounces back into space, thus cooling the planet further.

As man-made climate change warms up the Earth, key processes may shut down due to changes in the freshwater/salt water balance – the gulf stream, the ocean currents. If this happens and the poles are cut off from sources of warm air or water, then they may refreeze rapidly and the runaway ‘Snowball’ process can begin.

Evolving Out of Style

With all this talk of things that might happen in millions and billion of years it is probably prudent to mention that we almost certainly won’t be around anyway. If by the end of the world, you mean the end of civilization or the end of the human race, then even looking a million years ahead is foolish.

Even the most well-adapted and long-lived species seem to only last a few million years or so before evolving out of style. The ones that do are not exactly like us – crocodiles, sharks, cockroaches. The human race, like any other, is subject to the environment around it and will evolve and adapt with it. It only takes one big volcanic eruption or viral outbreak to change our circumstances dramatically.

In a million years we could have become plankton-eating aquamen or tree-loving, hairy cannibals. We may not even live on Earth anymore…

Big Crunch/Rip/Freeze

Our universe has been around for 13.7 billion years – Earth has been around for just over 4 billion. We’ve been here for a few hundred thousand – depending on what we you call ‘we’. If we do manage to secure our existence indefinitely – perhaps by uploading ourselves into machines or spreading ourselves far and wide enough into the cosmos – then can we really be here forever? Time it seems could be eternal but also it could not.

Following the Big Bang – the beginning of the universe – we can either live in an ever-expanding universe that eventually rips itself apart (the Big Rip), an ever expanding universe that gradually slows down (Big Freeze) or a universe that reaches some extremely large size and then begins to fall back in on itself (Big Crunch). It all depends on how the Universe is made up and how much dark energy there is.

If we’re heading for a Big Rip then eventually there will be no Universe left as we understand it – so we die. If it’s a Big Crunch then everything ultimately smashes back together and time end – so we die. If the Big Freeze happens then sooner or later all the energy in the universe gradually becomes so diluted and spread out that nothing energetically useful can ever happen – everything freezes out – (thoughts, movement, calculations) – so we die.

Heisenberg Uncertainty Principle

Nothing is impossible – just highly improbable. As fans of the Hitchhiker’s Guide are aware. That is what Heisenberg ended up stating about the Universe thanks to quantum mechanics. It is possible, though not very likely that a giant cat will appear one day and give the Earth a lovely hug and magic up some tea and cake. It is also equally unlikely that one day a giant death ray will appear and destroy our whole planet.

Given enough time – say an infinitely long time – eventually each of these things will happen. The problem is that since we already exist, it doesn’t matter if something good pops into existence alongside us. If something bad randomly blurts out of the vacuum – even for a brief moment – and destroys us then that does matter. The longer we hang around, the more chance there is for something like that to happen.

I'm Robert Simpson and I work at Google in London. I am the creator of <a href="http://dotastronomy.com">.Astronomy</a>. I am astrophysicist formerly of the <a href="http://zooniverse.org">Zooniverse</a> at the University of Oxford.